Processing of finely divided particulate materials

ABSTRACT

A mass of finely divided material is confined in a chamber. Two rollers are arranged for rotation in the chamber in axial parallelism with one another and define with each other a narrow longitudinally extending gap. At least one of the rollers has a circumferential wall composed of gas-permeable porous material. This one roller is hollow and arranged to communicate with a source of underpressure so that, as the roller rotates, the particulate material is attracted onto its outer surface forming a layer thereon which is subjected to substantial compaction when it passes through the gap between the two rollers. The rollers rotate in opposite direction. The compacted material is removed from the outer surface of the roller or rollers and subdivided into portions of desired size. A roller for use in the apparatus is disclosed.

United States Patent 1191 Reinhardt et al.

[ July 3,1973

[ PROCESSING OF FINELY DIVIDED PARTICULATE MATERIALS [75] Inventors:Helmut Reinhardt, Weiss near Cologne; Bernd Brandt; Albert Peters, bothof Wesseling-Berzdorf, all of Germany [73] Assignee: Deutsche Gold- UndSilber-Scheideanstalt vormals Roessler, Frankfurt am Main, Germany 22Filed: July 12, 1971 21 Appl.No.: 161,791

Related U.S. Application Data [62] Division of Ser. No. 874,654, Nov. 6,1969.

[30] Foreign Application Priority Data Nov. 8, 1968 [56] ReferencesCited UNITED STATES PATENTS Spencer 29/130 X Germany P 18 07 714.0

Primary Examiner-Alfred R. Guest Att0rney-Michael S. Striker 5 7 1ABSTRACT A mass of finely divided material is confined in a chamber. Tworollers are arranged for rotation in the chamber in axial parallelismwith one another and define with each other a narrow longitudinallyextending gap. At least one of the rollers has a circumferential wallcomposed of gas-permeable porous material. This one roller is hollow andarranged to communicate with a source of underpressure so that, as theroller rotates, the particulate material is attracted onto its outersurface forming a layer thereon which is subjected to substantialcompaction when it passes through the gap between the two rollers. Therollers rotate in opposite direction. The compacted material is removedfrom the outer surface of the roller or rollers and subdivided intoportions of desired size. A roller for use in the apparatus isdisclosed.

12 Claims, 2 Drawing Figures PATENTEUJUL3 I975 snmmrz PI V HIIIIATTORNEY PROCESSING OF FINELY DIVIDED PARTICULATE MATERIALSCROSS-REFERENCE TO RELATED APPLICATION This application is a division ofour application Ser. No. 874,654, filed Nov. 6, 1969 and entitledProcessing of Finely Divided Particulate Materials.

BACKGROUND OF THE INVENTION The present invention relates generally tothe processing of finely divided particulate materials, and morespecifically to the processing of such materials which requirespre-condensing and subsequent compacting of such materials into desiredshapes. The invention relates to an apparatus foreffecting suchprocessing and to a roller for use in the apparatus.

In many instances the processing of finely divided particulate material,such as pulverulent or finecrystalline and organic materials, frequentlydepends upon the possibility of increasing the volumetric weight of suchmaterials without destroying or adversely influencing their specificcharacteristics which depend upon the fine division of such materials.This is particularly true of highly dispersed surface-active'fillermaterials, such as silicium oxide, carbon black, aluminum oxide,aluminum silicates and calcium-silicates, all materials I which are usedin very large quantities in various industries.

The problems involved in the processing of these materials are notinsignificant. On the one hand, in their while the space required forstorage and transportation is substantially reduced, and dusting duringfilling, metering and processing is largely eliminated. It has beenproposed to achieve this by transforming the finely divided materialsinto agglomerates of certain configuration and dimension by subjectingthem to mechanical pressure. This has been found to be practical in acontinuous operation only if the significant quantities of gases presentin highly dispersed materials are first removed, because otherwise it isnot possible to obtain agglomerates with sufficient adhesion undermechanical pressure. it has been found, for instance, that it isimpossible to obtain the desired compaction and adhesion simply bypassing such materials between two metal rollers which subject them tomechanical compression. Therefore, gas removal and pre-condensing hasbeen resorted to, utilizing in known continuously operating apparatus ofthe type in question pressuretype conveyor screws, rollers or pairs ofrollers provided with radial projections or provided on the surface ofat least one roller with profiling. However, it has been found that thedegassing or outgassing effect and compaction obtainable with suchapparatus, which for the actual compaction utilizes a pair of pressurerollers,

is inadequate compared to the complexity and expense of the apparatusinvolved.

A further approach which has been tried is to deposit the material to becompacted onto hollow rollers, so-

called filter rollers, whose circumferential wall is gaspermeableandwhose interior is subjected to underpressure. The gas is therebywithdrawn from the deposited material and the material is supplied bythe filter rollers to the compacting gap between a pair of pressurerollers. Various modifications have been proposed for this basicapproach but in each case the gap between the pressure rollers-4n whichthe material is subjected to compaction-is fixed. This approach islimited in its applicability because it permits only the production ofcompressed blanks, as the compacted bodies made from the compactedfinely divided particulate materials will hereafter be called for thesake of convenience, without specific form and only within a ratherbroad range of grain sizes. A further disadvantage is that the compactedblanks obtained in this manner have a widely varying breakingresistance, a fact which is of particular disadvantage if the compactedblanks are of filler material which is intended for certainapplications, for instance for use in rubber mixtures, because with themixing procedure used in the production of rubber mixtures the compactedblanks can be broken down only partially to the original grain size. Theresult of this is an inadequate dispersal of the filler material and theresulting typical formation of pockets and cavities in the vulcanizedgoods.

In addition certain materials, for instance light reinforcing fillermaterials such as SiO can be compacted only to a bulk density ofapproximately 250 g/l in the apparatus known from the prior art andutilizing the socalled filter rollers, because the low mechanicalstrength of the fabrics used for the circumferential walls of the filterrollers makes it impossible to utilize higher compacting pressures. Thisis quite aside from the fact that even at these lowered operatingpressures the fabrics must be very frequently replaced.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to overcome the "aforementioned disadvantages.

A more particular object of the invention is to provide an apparatus forprocessing finely divided particulate materials which is not subject tothe disadvantages outlined before.

A concomitant object of the invention is to provide such an apparatuswhich enables continuous operation and the production of compactedblanks of specific desired shape and size with a defined narrow range ofbreaking resistance and increased bulk weight.

Still a further object of the invention is to provide a rollerconstruction for use in 'such apparatus.

in pursuance of the above objects, and others which will become apparenthereafter, one feature of the invention resides in the novel apparatusin which, briefly stated, a mass of finely divided material is confinedadjacent to the gas-permeable circumferential wall of a rotatable rollerhavinga hollow interior. The roller is thereupon rotated and subjectedin its interior to underpressure so as 'to attract the material bysuction to the same as to define with the latter a gap wherein the layeris subjected to compacting.

The roller having the gas-permeable circumferential wall, hereafter forthe sake of convenience called the filter roller, may rotate partiallyor completely in the material to be compacted, and the same is true ofthe other roller. The thickness of the layer may be maintained constantby removing excess attracted material from the layer before incrementsof the layer enter into the gap between the two rollers. In accordancewith the invention, one of the two rollers is bia'ssed towards the otherwith a biassing force which is preferably maintained at constant level.The other roller may also be a filter roller or it my be a roller havinga known gasimpermeable circumferential wall. In any case, the layer iscompacted on passage of the gap between the two rollers so as to bereduced by at least one half of its original volume and is deformedbyprofiling provided on the circumferential wall of at least one of therollersinto compacted blanks of desired shape and configuration anddefined range of breaking strength.

It is desired and advantageous according to the present invention thatthe dwell time of the material of the layer, that is of the material ofwhich each successive increment of the layer is composed which entersinto the gap between the two rollers, be below approximately 5 seconds,a time value which of course depends upon the roller circumference andthe speed of rotation of the rollers.

In accordance with the invention it is not necessary that two rollers beprovided having a gas-permeable or porous circumferential wall, or thateven two rollers of the same type be rotated oppositely one another. However, for granulating purposes it is desirable and preferable that oneof the two rollers has a profiled surface of circumferential wall.Depending upon the profiling, compacted blanks of certain configurationare obtained, for instance granules, little rods, tablets and the like.For instance, if the profile is half-moon shaped, then the compactedblanks will be similarly configurated. These compacted blanks may thenbe reduced to the desired dimensions in a cutting device of knownconstruction, for instance in a so-called rotary disc breaker. Becauseof the profiling on at least one of the rollers, at least two dimensionsof the resulting product are already established before the cuttingdevice acts upon the compacted blanks.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connecting with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is'a partially sectioneddiagrammatic perspective view of an apparatus according to the presentinvention; and

FIG. 2 isa partly sectioned somewhat diagrammatic perspective viewillustrating one embodiment of a roller for use in the apparatus of FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, theapparatus comprises a housing 1 having two transversely spaced walls111. Mounted in the housing 1 is a filter roller 2, for instance of thetype which will be discussed more specifically with reference to FIG. 2.The roller 2 is hollow, and arranged for rotation in axial parallelismwith the roller 2 is the roller 3 rotating in the direction opposite tothe roller 2, as indicated by the arrows respectively associated withthe two rollers. The circumferential wall of the roller 3 is notgas-permeable, and the roller 3 is therefore not designated as a filterroller as is the case with the roller 2. Instead, the circumferentialwall of the roller 3 is provided on its exterior with a half-moon shapedlongitudinal profile 4, shown in cross-section.

According to the invention the dimensions of the housing 1 are soselected that the spacing between the filter roller 2 and the housingwalls 1 in direction normal to the longitudinal axis of the filterroller 2 is substantially greater than the gap between the rollers 2 and3. v

The shaft 15 about which the filter roller 2 rotates is hollow and asuitable source of underpressure may be connected with it in order toobtain underpressure in the interior of the filter roller 2.

A measuring transducer 13a and a PI regulator which is coupled with anindicator device 13c, permit regulation of the value of underpressureapplied to the interior of the filter roller 2, via a valve 13c.

Slide bearings 9 journal the shaft 15 of the filter roller 2, permittingmovement of the latter in the direction towards and away from the roller3. Biass'ing devices 7, which here are illustrated as being of hydraulictype but which could be mechanically or pneumatically operated, act uponthe bearings 9 and bear upon a support structure which is locatedexteriorly of the wall 1a of the housing. A hydraulic pump 12a providesthe necessary biassing force whose value is registered on the indicators12b. If a pressure increase takes place in the system as a result ofchanges in the size of the gap between the rollers 2 and 3, caused byincreased thickness of the layer of material as it enters the gap or byother factors, the increased pressure can yield and fluid escapes intothe two reservoir bulbs 120 which are provided. Two pressure reliefvalves 12d are provided intermediate the reservoirs 12c and the biassingdevices 7 in order to assure that the applied "isodynamic pressure is soreduced only after it reaches a certain level. the manually operatedhydraulic pump 12a is replaced with an electrically operated pump, thena maximum-minimum or limit switch 12c must be provided for effectingautomatic regulation of the desired biassing pressure.

A hopper 14 communicates with the interior space 5 in thehousing 1 forintroducing into the space 5 the finely divided particulate materialwhich is to be compacted. When underpressure is applied to the interiorof the rotating'filter roller 2, the particulate material is attractedto the outer surface of the circumferential predetermined thickness, inorder to provide for as much thickness equalization-of the attractedlayer as possible before the same enters into the gap between therollers 2 and 3. The compacted material, having the configurationimparted to it by the profiling 4, falls out of the gap between therollers 2 and 3, and downstream of the gap it is cut to desired lengthsby the cutting device provided, here illustrated as a known disc breakeror rotary disc breaker 11.

FIG. 2 illustrates a specific embodiment of a filter roller for use inthe apparatus according to the present invention. Reference numeralidentifies the hollow shaft a portion of which is provided with bores15a. There are provided two side walls or end walls 17 of disc-shapewhich are gas-tight with the hollow shaft 15 at the opposite axial sidesof the region in which the bores 15a are provided. There is furtherprovided a circumferential wall 16 of cylindrical configuration which isprovided with a plurality of small bores or other apertures 16a. Thewall 16 is fluid-tightly connected with the end walls 17, for instanceby welding, and in the same manner the walls 17 may be connected withthe shaft 15.

Provided on the exterior of the cylindrical circumferential wall, whichmay also be called the inner circumferential wall 16, is an outercircumferential wall composed of a plurality of plates 18 of sinteredmaterial, for instances metallic sintered material, synthetic plasticsintered material or ceramic sintered material. These plates 18 abut oneanother and, insofar as they are composed of weldable material, arewelded to the inner circumferential wall 16 as well as to one anotherwhere they abut the welded seams 31. However, screw means 30 may also beprovided for securing the plates 18 to the inner circumferential wall16. The inner circumferential wall 16 is provided with interior radialreinforcing ribs 19 for increasing the strength and stability of theroller, but helically convoluted ribs or axially extending ribs 190 mayalso be provided, or any combination of the three. Reference numeral 20identifies the inlet opening of the hollow shaft 15 at whichunderpressure may be applied.

It has been found that the production of compacted blanks with definedrange of break resistance is facilitated by maintaining a constant levelof biassing pressure of the rollers 2 and 3 towards one another. Inorder to obtain only small fluctuations of this range it is advisable tomount one or both of the rollers inthe manner shown in FIG. 1, that isin such a manner that the gap width can change automaticallyindependence upon the thickness of the layer carried by the filter roller,,or the compaction of the material in the gap, or other factors, therebyassuring that the compacting and compression is always effected withidentical mechanical pressure. Furthermore, such a construction ofcourse reduces the possibility of breakdown of the apparatus. v

The level of this isodynamic pressure depends in each'individual caseupon the particulate material to be compacted, its moisture content andthe degree of compacting which is desired. in the case of white filtermaterials, such as silicium dioxide, the moisture content is'forinstance desirably not below l percent.

The optimum break resistance of the, compacted blanks made from a givenparticulate material depends upon the intended use and can readily bedetermined by empirical means. For instance, it has been found that SiO,granulates produced in accordance with the present invention haveadequate transport stability and maximum dispersion characteristics in atest rubber mixture if a break resistance to pressure between 100 and'500 pond (p) is obtained in he compacted blanks,

measured with the hardness tester, according to German Auslegeschrift1,374,254. The term breaking pressure is intended to mean the pressurein ponds which is necessary to abruptly destroy a granulate of 2 3 mmgrain size.

The dispersion characteristics of SiO compacted blanks made inaccordance with the present invention compacted silicium dioxide blanksisset to between 200 and 250 ponds, the dispersion in the test mixtureis substantially better than in the test mixture to which the siliciumdioxide powder was added.

For instance, if the original finely divided particulate material is aSiO powder with primary particle sizes smaller than-50 p. and with abulk weight of approximately g/l, then a SiOfgranulate according to thepresent invention and having breaking pressure values between 200 and250 ponds may beproduced unde approximately the following circumstances:

approximately 0.l 0.5 t/cm approximately 1 6 mm, up to approximately 4mm play in direction normal to the roller roller pressure roller gapaxes dwell time in the approximately 0.01 0.1 sec. 8 F underpressureapplied to filter roller gas penneability of the filter roller surfaceapproximately 0.3 0.95 kg/cm approximately 6 mlcm X i If the rollerdiameter is for instance 200 mm and the length of the rollers is 300 mm,the production amounts to approximately 250 kg/h granulate having a bulkweight of approximately 330 g/l. During the transportation of theparticulate material on the surface of the filter roller into the rollergap, that is prior to the com .pacting which takes place in the rollergap itself, a precompacting or precompressing to a bulk weight ofapproximately 250 g/l is obtained in this case.

If for instance one of the rollers' has a half-moonshaped longitudinalprofile in its outer circumferential surface with dimensions of 6 X 2mm, then a finished granulate with approximately the following screenanalysis is obtained by breaking the rod-shaped SiO compacted blanksfalling out of the gap between the rollers in a conventional rotary discbreaker and subjecting them subsequently to screen removal of the finessmaller than 0.5 mm;

Particle Size Enlarged photographs of the individual sieve or screenfractions of the finished granulate show that the form obtained for thecompacted blanks during compacting in the gap between the rollers isreadily visible in case of the fraction 3 mm, and that it is stillreadily identifiable in case of the fraction 2 3 mm. This means that theidentifiably shaped granulate quantity amounts to 65 percent, that isthe total of the fractions 3 5 mm and 2 3 mm.

It will be appreciated that unlike the embodiment illustrated in FIG. 1,it is possible to mount the filter roller 2 for rotation but not forshifting movement, and to mount the roller 3 for such shifting movement.However, the embodiment illustrated in FIG. 1 is preferred.

It is advantageous in accordance with the present invention that thepores. of the material of which the outer circumferential wall of thefilter roller is composed be so dimensioned that at a predeterminedoperational load of the suction device an underpressure of constantvalue in the interior of the filter roller, irrespective of whether thefilter roller is partly or completely immersed in the material to becompacted.

If, as illustrated in the embodiment of FIG. 1, a rotary .disc breakeris arranged below the gap between the rollers 2 and 3, then it isadvantageous that the cutting edges of the rotary'discs of the breakerextend in planes transversely to the elongation of the gap. This isparticularly advantageous if the apparatus according to the presentinvention produces compacted blanks in profiling which extendslongitudinally of the rollers.

The material for the porous outer circumferential wall of the filterroller is a suitable sinter material, such as sinter metal, sinteredsynthetic plastic or sintered ceramic. It is of course not necessarythat the outer circumferential wall consist of the plate-shaped portionsillustrated in FIG. 2, but this enhances the stability.

It is advantageous, but not absolutely necessary, that the spacing ofthe filter roller from the bottom wall of the housing 1 be at leastequal to half the roller diameter, and that the lateral spacing betweenthe sinter roller and the housing wall be equal to at least one rollerdiameter. The doctor blade mentioned before may be adjustably mounted soas to movable towards and away from the circumferential wall of thefilter roller, and it may also be so mounted that its angle with respectto the circumferential wall can be adjusted.

The pores of theporous material of the outer circumferential wall of thefilter roller may have a diameter of approximately 0 200 [1,, preferablybetween 0 35 p. The thickness of 'the outer circumferential wall shouldbe at least approximately 1 mm. At underpressures of 0.01 1.0 kg/cm thegas permeability of the outer circumferential wall of the filter rollermay be in the region between approximately 0.1 and 7 m lcm X h.

The roller for utilization in the apparatus according to the presentinvention, has certain very definite advantages over the roller used inknown apparatus, namely a long life irrespective of whether it isrotated at low or high rotational speeds, resistance to much higherpressure than are possible with the known constructions, and retentionof its shape, that is resistance to being deformed so it is out-of-roundin cross-section.

The following examples will further aid in an understanding of theinvention.

EXAMPLE 1 In an apparatus according to FIGS. 1 and 2 compacted blanks ofhighly dispersed surface active silicium dioxide were produced. Thestarting material, obtained by precipitation from an aqueous silicatesolution, had the following characteristics:

Dry loss (105) approximately 6% Specific weight 1.9 2.0 Bulk weight so 110 g/l Vibratory weight I60 200 g/l BET-surface 240 m Primary particle16 p. diameter The apparatus utilized an isodynamically biassed filterroller and a nonadjusted rotatable non-gas permeable counter rollerhaving half-moon shaped longitudinal profiling. Both rollers were 300 mmlong and had a diameter of 100 mm. The outer circumferential wall of thefilter roller was 5 mm thick andconsisted of sinter metal Siperm R(Remanit) having a maximum pore width of 35 .4.. The profile of thecounter roller had the dimensions 6 X 2. Arranged below the gap betweenthese rollers was a rotary disc type breaker with a spacing between thedisc of 3 mm.

Prior to operation of the device the housing was filled via the hopperto approximately two-thirds with the pulverulent material to becompacted, a roller pressure of 0.35 t/cm was set and an underpressureof 0.6 kg/cm was applied to the filter roller. The doctor blade arrangedabove the filter roller was set at a distance of 15 mm from thecircumferential wall of the filter roller. Thereupon, both rollers andthe disc type breaker were simultaneously started. The rotation of therollers was so regulated that the medium dwell time of the material tobe compacted in the gap between the rollers was approximately 0.15 sec.The width of the gap was approximately 1- mm. The movements of thefilter roller in direction normal to the axes of the two rollers, whichoccurred during the compacting operation, were in the range ofbetween l3 mm.

The bulk weight of the precompacted particulate material forming a layeron the filter roller prior to entering into the gap was 255 gl. Theoutput obtained was approximately 260 kg/h granulate having a bulkweight of 330 g/l. The breaking pressure of the compacted blanks wasbetween 200 and 250 pond.

After screening and classification to particle sizes between 0.5 5 mm,only a fine smaller than 0.5 mm amounting to 15 percent was left.

Sieve analysis on a laboratory sieve or screen of commercially availabletype showed the following values in the final product:

Particle Size The granulate portion having an identifiable shape(fractions 5, 3 5 mm and 2 3 mm) correspond to 62.6 percent of thetotal.

The dispersion ability of the granulates was tested in a red coloredtest rubber mixture free of vulcanizing additives. ABrabender-Plastograph was used as dispersion apparatus.

TEST MIXTURE AND DISPERSION CONDITIONS Vessel Utili- Mixing quantitiesvol. zation rpm Temp. time Components 3 ml ml C' min. Butyl rubber") 2828 50 50 10 Iron oxide batch 5 5 Kpl40(") 1.7 1.7 Granulate 20 10 Themixtures thus obtained were subsequently passed at 95 C and at a gapsetting of 1 mm three times through a laboratorytwo-roller frame andthen rolled out to a thickness of 5 8 mm. The quantity of dispersion wasthereupon determined under a light microscope, based upon top-lightedphotographs of microtome cuts taken of the rolled-out skin. No pocketsor similar irregularities were found. Surprisingly, the degree ofdispersion obtained with.the SiO granulates produced according to thepresent invention was even distinctly better than that obtained in testmixtures which were made with pulverulent starting material.

EXAMPLE 2 (COMPARISON TEST) The starting SiO material used in theExample 1 for producing granulates was pressed with a known apparatus ofcomparable dimensions. Precompression took place via a verticallyoperated screw and compacting took place in the gap between twooppositely rotating metal rollers whose circumferential walls wereprovided with wave-shaped serrations. In order to be able to at allobtain a granulate break resistance on the order of 2 pond it wasnecessary to pass the Si0 repeatedly through the gap between therollers. The production output was only 50 kg/h. The granulatedispersion in the test mixture produced in accordance with Example 1'was significantly poorer than that of the test mixture utilizing thepulverulent starting material. It was a particular disadvantage that thefines 0.5 mm obtained onclassification in the range between 0.5 mm was50 percent after the first compacting, and could be reduced toapproximately percent only by repeated compacting.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofapparatus differing from the types described above.

While .the invention has been illustrated and departing in any way fromthe spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can I by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

l.-- A roller for use in an apparatus for processing finely dividedparticulate materials, said roller comprising a hollow shaft having anelongated apertured portion; a 'pair of disk-shaped end wallsfluid-tightly mounted on said shaft at opposite axial ends of saidapertured portion; an apertured inner circumferential wall extendingfrom one to the other of said end walls concentric with said portion ofsaid shaft and fluidtightly connected with said end walls; and a porousouter circumferential wall mounted on and exteriorly surrounding saidinner circumferential wall and at least predominantly consisting ofsintered material.

2. A roller as defined in claim 1, wherein said material of said outerwall is selected from the group consisting of sintered metal, sinteredsynthetic plastics and sintered ceramics.

3. A roller as defined in claim 1, wherein said outer wall is composedof a plurality of abutting sections; and further comprising screw meanssecuring said sections to said inner wall.

4. A roller as defined in claim 1, wherein said outer wall is composedof a plurality of abutting sections which are welded to one another andto said inner wall.

5. A roller as defined in claim 1; and further comprising a plurality ofreinforcing ribs provided on said inner wall.

6. A roller as defined in claim 5, wherein at least some of saidreinforcing ribs extend axially of said inner wall.

7. A roller as defined in claim 5, wherein at least some of saidreinforcing ribs extend radially of said inner wall.

8. A roller as defined in claim 6, wherein at least some others of saidreinforcing ribs extend radially of said inner wall.

9. A roller as defined in claim 1, wherein said porous materialcomprises pores having diameters in the range between substantially 0200u.

10. A roller as defined in claim 10, wherein said pores have diametersin the range between substantially 0-35 p.

11. A roller as defined in claim 1, said outer circumferential wallhaving a thickness of at least 1 mm.

12. A roller as defined in claim 1, said outer circumferential wallhaving a gas-permeability of between substantially 0.1 and 7 m lcm whensubjected at one side to an underpressure of between substantially 001-1.0 kg/cm

1. A roller for use in an apparatus for processing finely dividedparticulate materials, said roller comprising a hollow shaft having anelongated apertured portion; a pair of diskshaped end wallsfluid-tightly mounted on said shaft at opposite axial ends of saidapertured portion; an apertured inner circumferential wall extendingfrom one to the other of said end walls concentric with said portion ofsaid shaft and fluidtightly connected with said end walls; and a porousouter circumferential wall mounted on and exteriorly surrounding saidinner circumferential wall and at least predominantly consisting ofsintered material.
 2. A roller as defined in claim 1, wherein saidmaterial of said outer wall is selected from the group consisting ofsintered metal, sintered synthetic plastics and sintered ceramics.
 3. Aroller as defined in claim 1, wherein said outer wall is composed of aplurality of abutting sections; and further comprising screw meanssecuring said sections to said inner wall.
 4. A roller as defined inclaim 1, wherein said outer wall is composed of a plurality of abuttingsections which are welded to one another and to said inner wall.
 5. Aroller as defined in claim 1; and further comprising a plurality ofreinforcing ribs provided on said inner wall.
 6. A roller as defined inclaim 5, wherein at least some of said reinforcing ribs extend axiallyof said inner wall.
 7. A roller as defined in claim 5, wherein at leastsome of said reinforcing ribs extend radially of said inner wall.
 8. Aroller as defined in claim 6, wherein at least some others of saidreinforcing ribs extend radially of said inner wall.
 9. A roller asdefined in claim 1, wherein said porous material comprises pores havingdiameters in the range between substantially 0-200 Mu .
 10. A roller asdefined in claim 10, wherein said pores have diameters in the rangebetween substantially 0-35 Mu .
 11. A roller as defined in claim 1, saidouter circumferential wall having a thickness of at least 1 mm.
 12. Aroller as defined in claim 1, said outer circumferential wall having agas-permeability of between substantially 0.1 and 7 m3/cm2 whensubjected at one side to an underpressure of between substantially0.01-1.0 kg/cm2.